1. Field of the Invention
This invention relates to oxytetracycline injectable compositions having increased antibiotic content.
2. Description of the Prior Art
Heretofore, preparations of oxytetracycline compositions suitable for injection have suffered from relatively high viscosities, poor stability and limited concentration of antibiotic. Such preparations have employed solvents such as propylene glycol, glycerol and polyethylene glycols as well as their mixtures with ethanol. High viscosities are particularly noticeable when injectable compositions containing polyhydric alcohols as solvents are used at low temperatures. Such high viscosities are often encountered when the compositions are used at the cool temperatures prevailing in barns, open feedlots or pastures. High viscosity compositions are objectionable because aspiration of a viscous composition into a hypodermic syringe and subsequent injection of the composition are both difficult and slow. Further, high viscosities also increase the time required to inject a large herd of animals. Other solvents may cause tissue irritation which is particularly undesirable in an animal as they may cause localized concentration of the antibiotic in the tissue and render the affected area undesirable for human consumption.
It is known according to U.S. Pat. No. 3,712,949--Greenbaum et al.--Jan. 23, 1973, to prepare injectable oxytetracycline solutions utilizing glycerol formal as the solvent, a water soluble magnesium salt such as magnesium chloride hexahydrate, antioxidant, buffering agent and water. These compositions overcome the disadvantages specified above, i.e., they are characterized as having lower viscosities at low temperatures and having excellent stability as to color, antibiotic potency and physical state. However, the maximum antibiotic concentration which has been achieved is approximately 15% by weight of the total composition. It is desirable to prepare compositions having greater antibiotic concentration. This is of great importance because a composition having a greater antibiotic concentration permits reduction of the number of injections at any one time in large animals such as cattle. In the case of a large herd, this reduces both time and labor. Additionally, a reduced number of injection sites in an animal brings about less damage to the quality of the meat.